Fabrics



g- 22, 1967 G. L. GOULDING ETAL 3,337,389

FABRICS Original Filed Sept. 29,. 1961 3 She ts-Sheet- 1 so EFFECT OFCONCENTRATION ALL TREATMENTS FOR 30 HOURS AT ROOM TEMPERATURE DEFFERENCEIN BREAKING LOAD BETWEEN CRIMPED AND UNCRIMPED 'FIBRES go o l I 0 IO 203O CONCENTRATION OF NoOH ' I? WW2.

EFFECT OF TIME ALL TREATMENT-S IN 20% w/x NoOH AT ROOM TEMPERATUREDTFFERENCE IN @HEAKIMG LOAD 6O @ETWEEN CRIMPED AND l I l l 0 I5 30 4 6O75 9O iO5 TIME OF TREATMENT INV NTORS ATTORNEYS Aug. 22, 1967 G. L.GOULDING ETAL 3,337,389

FABRICS Original Filed Sept. 29, 1961 3 Sheets-Sheet 3o DIFFERENCE INEREAKIN s LOAD BETWEEN CRIMPED AND EI=I=Ec'r OFTEMPERATURE UNCR'MPEDF'BRES TIME OF TREATMENT ADJUSTED To GIVE APPROX.EQUAL UNCRIMPED 0 I l II o 25 so 75 I I00 TEMPERATURE OF TREATMENT o I00 I r1614.

EFFECT OF TIME DIFFERENCE IN EA g LOAD 60 20%NOOH CONTAINING 7% QETWEENCRIMPED LAURYL-DIMETHYL QENZL AND AMMONIUM CHLORIDE AT UNCRIMPED FIBREsROOM TEMPERATURE.

INVENTORS I I I l l l o 0 I 2 a 4 5 N GFOFFHEYlfU/Yfllfi FUND/IV! K5177!PI L/P 8 7? W, (WM ATTORNEYS g- 22, 1967 G. L. GOULDING ETAL 3,337,389

I FABRICS Original Filed Sept. 29, 1961 3 Sh t -Sheet 3 FIG.5.

United States Patent 3,337,389 FABRICS Geoffrey Leonard Goulding andKeith Phillip Barr, Harrogate, England, assignors to Imperial ChemicalIndustries Limited, London, England, a corporation of Great BritainOriginal application Sept. 29, 1961, Ser. No. 141,791, now Patent No.3,287,787, dated Nov. 29, 1966. Divided and this application Mar. 29,1963, Ser. No. 274,370 Claims priority, application Great Britain, Sept.30, 1960, 33,612/ 60 9 Claims. (Cl. 161-75) This invention relates tothe manufacture of improved fibres and fabrics made therefrom.

This application is a division of our copending application, Ser. No.141,791, filed Sept. 29, 1961.

Some fabrics containing staple fibres of natural or synthetic originparticularly when made from polyesters such as polyethyleneterephthalate show a tendency to form small balls of fibres or pills ontheir surface, due to wear. The propensity of forming such balls offibres during wear is known as pilling and is believed to be associatedwith the migration of the fibres which are not firmly held in positionin the yarn or fabric. Pilling is therefore encountered in low twistyarn and in loosely woven or knitted fabrics containing such yarns, whenmade from polyester fibres.

It is an object of our invention to provide improved fibres which can bemade up into fabrics in which pilling is reduced or at least becomesless noticeable, even when low twist yarns and loosely woven or knittedfabrics containing such yarns are used. We have made the observationthat polyester fibres can be weakened at intervals by chemical means ifthey have been deformed by crimping so that they subsequently breakunder mechanical stress e.g. as encountered during wear of the fabric.As a result any loosely held fibres which migrate to the surface of thefabric are broken ot the weakened intervals and the formation of pillsis eliminated or reduced and any pills which are formed can be easilyremoved from the fabric surface by appling mechanical stress egg. bybrushing.

It is another object of our invention to produce tows of polyesterfilaments which can be converted into tops by a stretch breakingprocess, known as tow to top-conversion, in which the forces necessaryfor breaking the filaments are less and breaking is facilitated.Overlengths during cutting are eliminated.

The invention is illustrated in part by the drawings which are graphsshowing the effects of variables in the chemical treatment includedtherein.

FIGURE 1 shows the effect of concentration;

FIGURE 2 shows the effect of time;

FIGURE 3 shows the effect of temperature; and

FIGURE 4 shows the effect to time when a quaternary ammonium salt isincluded in the bath;

FIGURE 5 is a diagrammatic plan view of a part of a polyethyleneterephthalate filament beig strained by bending, the view being usefulin imparting an understanding of the point of selective pronouncedattack of the chemical agent according to the present invention.

According to our invention, we provide improved crimped filaments andfibres characterised in that they have been weakened at intervalscorresponding substantially to the apexes of their crimp when the crimpis caused by a permanent deformationinvolving compression beyond 1 to 2%of the elastic limit on the inner curvature of the bent filament orfibre. Preferably the fibres have 5 to '18 crimps per inch. It is alsopreferred that the fibres should be reduced in strength by at leastone-third at the apexes of their crimp, compared with the stronger fibreportions between said weaker portions.

We also provide a process for making such filaments and fibres whereincrimped synthetic polyester filaments or fibres are treated with achemical agent under conditions such that the filaments or fibres areweakened at intervals corresponding to the apexes of their crimp. Theprocess is preferably applied to filaments in the form of a crimped,drawn two before the filaments have been subjected to a heat settingprocess for setting the imparted crimp and before cutting or breakinginto staple fibre.

Many chemical agents may be used, the most convenient are alkalinesolutions such as sodium hydroxide solution, ammonia, solutions ofcertain quaternary ammonium salts or methyl alcohol, which may be addedto the sodium hydroxide solution, or certain diamines such as a solutionof hexamethylene diamine, anhydrous glycols including high molecularweight glycols their esters and ethers, which are still liquid at roomtemperature. Inert diluents may be added to these solutions if desired.

Our invention also provides improved fabrics characterised in that theycontain at least. a proportion of crimped polyester fibres which areweaker at intervals corresponding substantially to the apexes of theircrimps. Such fabrics have a reduced propensity of pilling even when theyare made from yarns or using fabric constructions, which when made fromor applied to yarns of unweakened fibres, show a marked propensity topilling.

A treatment of uncrimped filaments or crimped but heat set filamentsunder the same conditions does not lead to the same weakening at spacedintervals along the lengths of the filaments or fibres, because thechemical agents attack more uniformly. It should be appreciated that theweakening or breaking of the filaments or fibres by our treatment is adirect consequence of the selective intensity of the attack caused bythe agents at intervals along the filaments or fibres at the apexes ofthe crimps, whereas the portions between the apexes are affected to alessor degree or may remain substantially unaffected by the uniformapplication of the chemical agent. As a result the portions of thefilaments or fibres treated with a suitable agent break under mechanicalstress preferentially at intervals whereas the portions between mayremain substantially unaffected in strength.

It is believed that the selected weakening at the apexes of the crimpsis brought about by internal stresses causing local disorder in thefilaments or fibres imparted by the acute deforming operation duringcrimping. For this reason stutter box crimping and gear crimping arepreferred.

The conditions of treatment have to be determined by experiment andshould be selected so that no intolerable weakening of the filaments orfibres should occur in the uncrimped portion, whereas the apexes of thecrimps are weakened by at least one third or preferably by about onehalf or more, compared with their original strength. This can be done bymeasuring the tenacity of a small sample of the filaments or fibresbefore and after the treatment and by examining the broken ends of thefibres which should occur only at the apexes of their crimp.

The strains introduced during crimping should preferably be such as tocause bending of the filaments at defined intervals and which results ina permanent deformation involving compression beyond l%2% of the elasticlimit on the inner curvature of the bent filament and a tension on theouter curvature of the bent filament to cause a deformation not beyond5% of the elastic limit, only at intervals along the filament axis. Inthe case of polyester filaments having a substantially circularcrosssection the deformation should preferably involve bending thefilaments at intervals to a curvature which is less than 50 times thefilament diameter, e.g. a 4 denier filament should be bent to a radiusof curvature of less than 2 times cm. Conditions of crimping shouldpreferably be arranged so that the intervals between crimps result in518 crimps per inch. If the crimp frequency is below 5, the crimpedfibres which migrate to the surface of the fabric may cause the fibresto be broken oif at intervals which are too large to prevent theformation of pills. In other words the projecting broken fibre ends willbe too long to prevent the formation of pills. If on the other hand thecrimp frequency is allowed to rise above 18 crimps per inch, the usefullengths of fibre between the apexes of the crimps may be too short andfabrics made from such fibres are likely to have a reduced resistance toabrasion and wear and therefore will deter from their commercial value.

For a better understanding of the above requirements we refer to FIG. 5showing a diagrammatic plan view of a part of polyethylene terephthalatefilament being strained by bending. In FIG. 5 a filament of diameter dis being strained by bending to a radius r such that a small part of thefilament AB, which part is of the order of the filament diameter d,subtends an angle at the centre of curvature. At the inner curvature ofthe filament, compression beyond 1%2% will cause a permanent deformationand disorientation of the fibre forming polymer. This is believed topermit the selective pronounced attack of the chemical agent comparedwith the remaining portions of the fibre, because of a reduction in theorder of the filament structure in the bent portion.

On the outer curvature an elongation occurs which causes furtherorientation. Because of this, the disorientation at the inner curvatureof the bent filament, the latter becomes prone to greater attack by thetreating agents. 0n the outer curvature bending will cause orientationwhich may be accompanied by crystallisation and for r The desired crimpmay be obtained using a stutter box crimper having relatively largediameter feed rolls and by adjusting the pressure in the stutter boxfrom which the exit of the crimped filaments is restrained by means of adead weight or by hydraulic pressure. We have found feed rolls of 46diameter about 1 wide suitable for the crimping of tows of100,000-300,000 denier, in a stuffer box crimper.

It should be appreciated that a uniform application of the chemicalagent is necessary in order to obtain the selective weakening of thefilaments according to our invention. Strong aqueous caustic alkalisolution of 2030% by weight, may be used at low temperatures, forexample at 20-40 C., for a treatment lasting 30-50 hours. The additionof small amounts of catalytic accelerators to the caustic alkalisolution selected from methyl alcohol and certain quaternary ammoniumsalts, speed up the reaction. Suitable quaternary ammonium saltscomprise e.g. cetyl trimethyl ammonium bromide and lauryl dimethylbenzyl ammonium chloride. The eflfect of other quarternaries such ascetyl tri'methyl pyridinium bromide, dimethyl phenyl benzyl ammoniumchloride and tetramethylammonium bromide is less marked, and because ofthe additional cost to the treatment they are therefore not recommended.With the addition of the accelerators the concentration of the causticalkali solution may be considerably decreased e.g. to 5% by weight or aslow as 1%. Using temperatures near the upper limit as specifiedhereafter, the time of the treatment may be drastically reduced. Quitesmall amounts of the accelerator are suitable e.g. 0.005% to 1% byweight of the solution, as described in our copending US. Patent No.3,135,577. It must be emphasised, however, that the treatment should becarried out at a temperature below heat setting temperature to obtaineffective treatment. It will be appreciated that the time of treamtentcan be shortened as higher temperatures are used, but since theselective degradation of the crimped filaments decreases with increasingtemperature, temperatures below 110 C., preferably room temperature upto about 70 C. are preferred.

In the case of crimped filaments having an overall tenacity above 4 gms.per denier the tenacity should be reduced preferably below 3 and above1.5 g.p.d. In the case of medium tenacity fibres below 4 gms. per denierit is desirable to reduce the overall fibre tenacity to 2.5 gms./ denieror below but above 1.0 gm. per denier. It will be appreciated that acertain amount of reduction in the tenacity even in the stronger fibreportions, between the crimps, is tolerable but this should preferablynot exceed /3 of the initial tenacity. In the case of the treatment withcaustic alkali a loss in weight of up to 10% with a correspondingreduction in the diameter of the filaments may be brought about and thisis associated with an improved handle of the fabric.

Our invention will more particularly be described relating to polyesterfilaments and fibres made from polyethylene terephthalate for which itisparticularly suitable, the filaments having a substantially circularcross section. It will be appreciated, however, that our invention isnot intended to be so limited and that it applies also to filaments andfibres having a non-circul ar cross section, particularly =a cruciform,Y-shaped, tri-lobal, dog-bone, or any other known cross section forthermoplastic filaments. Similarly it will be applicable to otherpolyester or c0- polyester filaments as stated herein and which show apropensity to pilling.

Preferably polyethylene terephthalate filaments are produced by aprocess of melt spinning followed by drawing at a temperature below 110C. preferably between and 98 C. The drawn filaments in the form of towsare then subjected to a stufier box crimping operation ensuring adeformation in the filaments to cause bonding at intervals to acurvature which is less than 50 times their filament diameter in orderto impart the desired crimp, at a frequency of between 5 to 18 crimpsper inch, depending upon the filament diameter which may be between 1 to5 denier per filament.

The crimped tows are then subject to the treatment with the definedchemical agents which are removed by e.g. neutralising with dilutestrong acid solution, rinsing with water, followed by drying and heatsetting at a temperature above C., preferably using steam atsuperatmospheric pressure and temperatures between l30150 C., andtemperatures up to 220 C. using dry heat. Setting is necessary to bringresidual shrinkage in boiling water for 1 minute, to less than 1%.

Suitable finishing lubricants may be applied before or after heatsetting in order to facilitate processing and to prevent theaccumulation of static electricity. The crimped, treated and heat settows are then out into staple fibres of the desired length, e.g. between1 /2" and 7".

From these staple fibres improved fabrics can be produced by knownmethods comprising weaving and knitting su'ch fabrics have a reducedpropensity to pilling.

We also provide a new type of synthetic polyester fibre having 5-18crimps per inch and an overall tenacity of 2.5 gms. per denier or below,but above 1.5 g.p.d., the tenacity of the stronger portions of thefibre, between the apexes of the crimp, being only up to A less than theinitial tenacity of the drawn fibres. By comparsion the drawn crimpedfibres have a tenacity of 4 gm. per denier and up to 6 gm. per denier,before the treatment with the chemical agent.

The polyester filaments and fibres referred to in this specification aremade by a process of melt spinning and denote fibre forming polyestersincluding polyethylene terephthalate, copolyesters derived from up to15% of another component which may be selected from the group ofdicarboxycylic acids having the formula:

where R may be methylene, polymethylene or a'rylene, other thanparaphenylene, represented by a sebacic, adipic and isophthalic acid,and the remainder polyethylene terephthalate; or modified fibre formingpolyesters such as poly (hexa hydro-paraxylylene) terephthalate.

The filaments may be subjected to a deformation step which is effective,followed by the treatment with a suitable agent and if desired followedby further steps such as heat setting before or after furtherdeformation steps to bring about a greater crimp frequency. Thefilaments need not be cut and may be made up into fabrics from ourtreated filaments in the form of filament yarn.

If the filaments or fibres in their specified crimped condition are tobe treated in fabric form, no heat setting of the imparted crimp musttake place after crimping and prior to the treatment.

The polyester filaments may be subjected to immersion or spraying withhot substantially anhydrous polyethylene glycols and nonyl phenylpolyethylene glycol ethers, of a molecular weight of 200-2000, usingtemperatures above 80 C. but at least C. below the melting temperatureof the polyester, preferred temperatures are 110-130 C. The polyglycolsmay be applied before or after drawing of the polyester filaments andthis brings about a considerable improvement in dye uptake. One suchapplication of polyglycols is described in our copending US. applicationSer. No. 114,021.

The following examples in which all parts and percentages are by weightillustrate but do not limit our invention.

EXAMPLE I steam at 130 C., and cut into staple fibres of any desiredlength. When a number of filaments from the treated tow are tested in atensile testing apparatus, it is found that breakage occurs always atthe apex of the crimp, and the single fibre tenacity compared with anuntreated control is reduced by 94%. Fabrics containing the treatedstaple fibres show no pilling, whereas fabrics containing untreatedfibres show numerous pills.

The single fibre tenacity of crimped tow which is heat set using steamat 140 C. for half an hour, before the treatment with the sodiumhydroxide solution in Example I, is reduced by only 32%.

6 EXAMPLE II A tow of polyethylene terephthalate filaments is crimpedand the crimped tow treated with sodium hydroxide solution and washed asin Example I. The treated tow is converted into top or yarn by a stretchbreaking process designed to give the desired staple length between 2%and 6 inches.

Conversion of the tow into top or yarn is facilitated as lowerstretching forces are required, because the alkaline treatment hasproduced positions of low tensile strength at the apexes of the crimpsand the tow will break to give the required fibre length more easily.Undesirable overlengths and underlengths in the staple fibres willtherefore be absent.

In the following Examples III to V1, experiments are described toillustrate the effect of setting on a simulated crimp in polyethyleneterephthalate yarn under various treating conditions with caustic sodasolutions, with and without an accelerator, and the testing method usedfor determining the breaking load and extension of the yarn.

Yam-Polyethylene terephthalate 75 denier 36 filament yarn having atenacity of 4.5-5.5 g.p.d. and an extension at break of 27-17%.

Crimping-The yarn was wrapped round a 2 centimeter wide strip of copperfoil 0.25 mm. thick, placed between polished steel plates and subjectedto a pressure of 15 tons per square inch for five minutes in a hydraulicpress, to obtain a simulated crimped yarn, in which each filament isdeformed by compression beyond the elastic limit on the inner curvatureof the bent filaments, when the elastic limit is between 12%.

Setzing.-The yarn was subjected to dry heat setting by a treatment in anelectric oven at 140 C. for ten minutes. Other samples of the same yarnwere subjected to steam setting in a Sanderson oven at a steam pressureof 40 lbs. per square inch, equivalent to a temperature of 140 C., forfifteen minutes.

Treazment.-The crimped yarn, set or not set as required, was placed withan uncrimped control in a ml. flask and treated as described. After thetreatment the samples were washed thoroughly in water and dried.

Testing-Lengths of yarn containing one crimp only were mounted on cards,the crimp position marked and the fibre breaking load and extension atbreak were determined on an Instron tensile tester. Figures quoted inthe following tables are the mean of ten tests.

The uncrimped controls were tested similarly.

EXAMPLE III Efiect of setting the crimps.-The results are shown in usinga 20% w./v. sodium hydroxide solution at room temperature. Unset, driedheat set, and steam set yarns both crimped and uncrimped were tested forbreaking load and extension at break both before and after the treatmentwith caustic soda. It will be seen from the table that the effectobtained produces considerable differences in tensile strength betweenthe crimped and uncrimped portion of the filaments and that this effectis achieved with the unset fibre where, after treatment, the crimpedfibre was 48% weaker than the uncrimped fibre. The set fibres do notshow this significant strength difference.

Dry heat set fibre differs by approximately 6% between crimped anduncrimped samples, both before and after treatment. Crimped steam setfibre was twice as weak compared with an uncrimped sample, aftertreatment as before the difference was still only 21%. V

In every case the unset treated samples broke at the crimp when tested,whereas the controls and also the set crimped samples did not alwaysbreak at the crimp. A sutficient number of tests have been made toconclude that weakening occurs preferentially at the apex of the crimpin the case of unset filaments.

9 EXAMPLE VI Polyethylene terephthalate yarn was treated at roomtemperature with 20% sodium hydroxide solution to which 1%lauryl-dimethylbenzyl ammonium chloride, available under the trade nameVantoc C.L., had been added. The results of the treatment during one toseven hours on uncrimped and crimped filaments is shown and,

It will be seen from the examples that:

1) Unset crimped fibre is preferentially attacked at the crimp apexes bystrong aqueous caustic soda solution.

(2) Both steam and dry heat-set crimped fibres do not undergo thispreferential attack to the same extent.

(3) Addition of quaternary ammonium salts to caustic soda solutionaccelerates the rate of attack.

(4) Fabric made from treated fibre shows an improvement in pillingperformance compared with untreated fibres.

Although in the preceding examples polyethylene terephthalate filamentsand fibres have been used, it is believed that similar effects areobtained with other commercially available crimped oriented hightenacity synthetic polymer filaments or fibres such as nylon, Perlon andpolypropylene, provided that the treatment is carried out with asuitable agent which will attack at the apexes TABLE 5.-EFFECT OFACCELERATOR (See also FIG. 4.)

[Unset yarn treated at room temperature with w/lv b31011 containing 1%lauryldimethylbenzylammonium Unerimp'ed Crimped Percent Difierenoe Timeof Treatment (hours) Breaking Extension Breaking Extension BreakingExtension Load Load Loa EXAMPLE VII This example illustrates the effectof the treatment on pilling. A stuffer box crimped unset drawnpolyethylene terephthalate tow was treated for thirty hours in 20%aqueous sodium hydroxide solution at room temperature, washed withwater, dried, set in air at 140 C. for 10 minutes, cut into 2 inchlengths and resulting staple fibres were converted on standard cottonequipment to give spun cotton type polyester yarn and this was woveninto a twill fabric which was tested for pilling.

Table 6 shows the properties of the fibre at various stages of fabricproduction, compared with untreated polyester cotton-type 2" long staplefibres. It will be seen that improved pilling performance is achieved atthe expense of decreased flex abrasion resistance and tensile strength.The lower extension at break of the treated fibre is of particularadvantage if the fibres are blended with cotton.

of the crimp and when the crimp has been obtained by bending undercompression beyond the elastic limit and not set, so that the filamentsand fibres are weakened at intervals corresponding to the apexes oftheir crimp.

The Brush and Sponge test referred to in Example VII is described inA.S.T.M. 1958 D. 1375T, page 515. This test is intended to determine theresistance of woven fabrics to pilling and fuzzing. The method providesa laboratory procedure for mechanically simulating wear conditions byfirst brushing a fabric to form free fiber ends and then subjecting thefabric to a circular rubbing ac tion with a sponge Which rolls the fiberends into pills.

The terms fibre and filament are used substantially interchangeablyherein in instances where no intended distinction is evident from thecontext.

What we claim is:

1. An oriented synthetic polymer fibre oriented along substantially thewhole length thereof having 5-l8 intervals per inch throughout thelength thereof of reduced TABLE 6.FABRIG PRODUCTION Production DetailsFibre Form Prope ty Units Untreated Treated Fibre Fibre Cut fibre Fibrelength Inches 2 2 Denier 3 3 'Ienae1ty G.p.d 5. 37 2. 38 ExtensionPercent 30 18 Spinning fibre spun into Singles yarn (1/18.7's); TenacityG. d

2/18.7s cc. yarn with 10Z Doubled yarn (2/18.7s). Extension-.- Pei censingles and 5S doubling 'Ienaci y God... 2. 77 1 45 twist, ExtensionPercent 32. 2 1'7. 9

Weaving yarn woven into a Finish fabric Pilling (sponge test 200 P 2 2twill fabric 32' wide Ins/Sq m 28 8 52 x 52 ends x picks/inch finishedsett.

Flex abrasion N o. of flexes to break 6, 000 1, 800

Flat abrasion Similar diameter compared to the remainder of the fibrebetween said intervals, each interval being on the order of two timesthe fibre greatest diameter in extent, lengthwise of the fibre; thetenacity of said fibre in said intervals being Within the range ofgreater than 1.5 and less than 4 grams per denier, the tenacity of saidfiber between said intervals being within the range of greater than 2 /3and no greater than 6 grams per denier and being substantially greaterthan the tenacity of said fibre in said intervals.

2. The oriented synthetic fibre of claim 1 wherein said fibre has 5-18crimps per inch throughout the length thereof, each of said intervalsbeing coincident with the apex of a respective crimp of said crimps.

3. The oriented synthetic fibre of claim 2, having a substantiallycircular transverse cross-sectional shape between said intervals, eachcrimp radius of curvature being less than 50 times the greatest filamentdiameter in the remainder of said fibre.

4. Yarn comprising the fibre of claim 2.

5. Textile fabric comprising the fibre of claim 2.

6. The oriented synthetic fibre of claim 2 in which the fibre comprisesa polyester.

7. The oriented synthetic fibre of claim 6, wherein the polyesteressentially comprises polyethylene terephthal- 12 ate and up to 15percent of another polyester chosen from the group consisting ofpolyesters derived fromv bicarboxylic acids having the formula:

HOOCR-COOH where R is a member of the group consisting of methylene,polymethylene, and poly (hexa hydro-para-Xylene) terephthalate.

8. The oriented synthetic fibre of claim 1 having an overall tenacity ofbetween less than 3 grams per denier and more than 1.5 grams per denier.

9. The oriented synthetic fibre of claim 8 having a fineness of Withinthe range of 0.9-5 denier.

Review of Textile Progress, The Textile Institute, Manchester, England,pub. 1957, vol. 8 (1956), TS 1300 R4.

ALEXANDER WYMAN, Primary Examiner.

G. D. MORRIS, Assistant Examiner.

1. AN ORIENTED SYNTHETIC POLYMER FIBRE ORIENTED ALONG SUBSTANTIALLY THEWHOLE LENGTH THEROF HAVING 5-18 INTERVALS PER INCH THROUGHOUT THE LENGTHTHEREOF OF REDUCED DIAMETER COMPARED TO THE REMAINDER OF THE FIBREBETWEEN SAID INTERVALS, EACH INTERVAL BEING ON THE ORDER OF TWO TIMESTHE FIBRE GREATEST DIAMETER IN EXTENT, LENGTHWISE OF THE FIBRE; THETENACITY OF SAID FIBRE IN SAID INTERVALS BEING WITHIN THE RANGE OFGREATER THAN 1.5 AND LESS THAN 4 GRAMS PER DENIER, THE ENACITYOF SAIDFIBER BETWEEN SAID INTERVALS BEING WITHIN THE RANGE OF GREATER THAN 22/3 AND NO GREATER THAN 6 GRAMS PER DENIER AND BEING SUBSTANTIALLYGREATER THAN THE TENACITYOF SAID FIBRE IN SAID INTERVALS.